1. 根目录:
2. include
3. linux
4. netfilter_defs.h

#ifndef __LINUX_NETFILTER_CORE_H_
#define __LINUX_NETFILTER_CORE_H_

#include <uapi/linux/netfilter.h>

/* Largest hook number + 1, see uapi/linux/netfilter_decnet.h */
#define NF_MAX_HOOKS 8

#endif